Mikhail Khodorkovsky looks from behind glass at a court room in Moscow in December 2010. Khodorkovsky was released today, after spending the past 10 years in prison on politically tinted charges of tax evasion and embezzlement.

In a statement posted on his website, Mr. Khodorkovsky, the founder of the now-dismantled oil company Yukos, said that he had requested a pardon over a month ago and that he was “happy for a favorable decision.”

“I would like to thank everyone who followed the Yukos case for all these years and for the support, which you gave to me, my family and all those who were unfairly convicted and continue to be persecuted," he was quoted as saying.

The sudden release of the former oil tycoon and billionaire, together with a sweeping amnesty of thousands of prisoners, including many of the most prominent cases deemed political by critics – such as the two members of the punk rock group Pussy Riot and 30 Greenpeace activists – has ignited a debate about what it all means.

Pessimists argue that the amnesty is a one-off concession aimed at defusing criticism of Russia's human rights record in the run-up to the Sochi Winter Games, on which Mr. Putin has staked his own prestige, his country's image, and at least $51 billion in investments mostly ponied up by the government and top state corporations. Once the Games are over, they say, Putin's crackdown will return in full force.

"What does the West know about Russia? Only that it's the country where they keep Khodorkovsky and the Pussy Riot girls in prison," says Gennady Gudkov, who was expelled from the Duma last year over his links with the anti-Kremlin protest movement.

"Now they are all amnestied, and this can be described as a very effective PR move aimed at Western public opinion. Khodorkovsky's sufferings are over, thanks to Putin. But I wouldn't say it signals any change of course," he says.

Optimists recall historical precedents to point out that mass prisoner releases have more than once heralded sweeping reforms. This could be Putin's intention in setting free so many high-profile prisoners at once.

"I've been expecting this for two years now. It is not a temporary thaw, because there will be no more frosts," says Ella Pamfilova, a veteran lawmaker, former minister of social affairs, and human rights campaigner.

"This country is evolving, people and society have changed, and the authorities have to take that into account. ... So we may predict that this process will go on developing and growing after the Olympic Games have ended," she says

Ms. Pamfilova employed the word "thaw" in describing this development, a term that evokes the period of tectonic social changes that accompanied Nikita Khrushchev in the mid-1950s. Mr. Khrushchev began his systematic efforts to reform the Soviet system with a mass prisoner release that virtually emptied the Stalin-era Gulag camps.

More recently, the last Soviet leader Mikhail Gorbachev kicked off his perestroikacampaign to democratize the Soviet system by freeing the USSR's most famous dissident, scientist Andrei Sakharov, from internal exile and bringing him to Moscow, where he subsequently became politically active. Some optimists hint that Khodorkovsky, too, might return to the political stage and become a focus for liberal opposition.

Other experts say such parallels are of limited value, because Russia is a vastly different country from the former USSR, and because Putin, despite his authoritarian tendencies, does not preside over a totalitarian system.

Khodorkovsky and the Pussy Riot band members were imprisoned after receiving public trials. Critics called them political prisoners, arguing that they were victims of selective justice, subjected to legally dubious trials that were enforced by state-orchestrated courts. There is a great deal of evidence to back up those criticisms, but it may still be a stretch to compare Khodorkovsky, a former oligarch who made his fortune through shady dealings in the freewheeling 1990s, with Nobel Prize-winning Mr. Sakharov, who was exiled on orders from the Communist Party.

Henry Reznik, one of Russia's best-known defense attorneys who heads the Moscow Bar Association, says that despite all the complexities of Putin's Russia, it is not comparable to the former Soviet Union.

"There is no Gulag, no mass repressions. There exists freedom of movement and freedom of speech," he says.

Mr. Reznik suggests that the mass amnesty reflects a degree of recognition on the part of Russian authorities that many inmates, including Khodorkovsky and the Pussy Riot detainees, have not received fair trials.

In Russia, "politics does make pressure on the judicial system, and convictions often have nothing to do with the law," he says.

"But in the case of the Greenpeace activists, amnesty was the only form the authorities could find to get out of the scandalous situation they had put themselves into."

The Greenpeace activists were arrested in September as they tried to hang a protest banner on an Arctic oil drilling rig. They were initially hit with the harsh charge of piracy, before prosecutors backed off and filed hooliganism charges instead.

Mr. Reznik says the two trials of Khodorkovsky actually canceled each other out. In the first trial, Khodorkovsky was accused of not paying taxes. In the second, he was convicted of stealing the property that he hadn't paid taxes on.

"It's really absurd. The longer this case went on, the more our authorities understood that its negative impact outweighed any benefits they were gaining," he says.

Vladimir Ryzhkov, a former lawmaker who co-chairs a newly-registered liberal opposition party, recently met with Putin at a Kremlin roundtable. He says the president carefully listened to criticism of policies such as the law against gay "propaganda" and a crackdown on foreign-funded civil society groups. Both initiatives, Ryzhkov says, cater to the prejudices of Russia's conservative majority while alienating the country's educated and liberal-minded middle class.

There is little evidence that Putin has changed his mind, however, he says.

In two major public appearances in the past week-- his annual state-of-the-nation address and a marathon televised press conference-- Putin appeared to double down on his concept of Russia as a bastion of social conservatism.

"I take the amnesty, and other recent changes, as evidence that the authorities want to change the mood without embarking on any systematic political reform," Mr. Ryzhkov adds.

Some experts contend that Putin is actually moving to build a more authoritarian system. In this case, releasing prisoners is probably more a sign of confidence in his own supreme power than a concession to outside opinion or internal pressure to liberalize.

"Before 2011, Russia had a soft authoritarian regime," says Liliya Shevtsova, a veteran political expert with the Carnegie Center in Moscow. "Today, after a lot of repressive legislation was passed, it's a tough authoritarian regime that has taken on the ability to interfere in the private lives of citizens, which is what the anti-gay law actually means."

"The release of Khodorkovsky and the others may serve some practical purposes, but it does not portend any kind of thaw," she adds. "There is absolutely no whiff of political liberalization in the Moscow air."